1. Field of the Invention
The present invention pertains to disc-type valves generally comprising a generally tubular valve body and a disc-like valve element disposed in the flowway formed by the valve body and rotatable about an axis transverse to that of the flowway to open and close the flowway. Rotating with the valve element are a shaft or a pair of stub shafts mounted in the valve body and an operating handle. A positioning member or assembly is provided and the handle can be latched to the positioning member to hold the handle, shaft, and valve element in any one of a number of positions.
2. Description of the Prior Art
In prior art valves of this type, the various rotating parts are typically connected to one another by connection members such as keys, pins, screws, non-circular drive components, etc. for joint rotation. This permits shipment of the valve in disassembled form, assembly in the field, and disassembly and re-assembly for maintenance purposes. However, this conventional approach also introduces problems. In particular, the above-described means of connection of the rotating parts involves a high degree of susceptibility to undue play between the parts. This is compounded by play between the handle and positioning means when the two are latched together to hold the valve in a given position. In an attempt to combat this effect, precisely controlled machining procedures have been used, and these increase the cost of manufacture of the valve. Also, special tools are required to tighten the connections between the parts after they have been assembled by hand by the user. This further increases the expense as well as the installation time.
Other problems are introduced by the fact that there must be some clearance between the rotating parts to permit hand assembly. Furthermore, the use of connecting members such as keys, pins, etc. increases the number of parts. Thus in opening and closing the valve, torsional leads are carried by the connecting members across the clearances. This weakens the assembly, for example by reducing the capability of the disc, carried by the shaft, to act as a beam in closed position. During use, and particularly disassembly and re-assembly, the parts become worn thereby increasing the clearances. The problem is further complicated by the fact that the clearances tend to compound vibrations caused by turbulent, high velocity flow. The result may be premature valve wear and even catastrophic failure.